1. Field of the Invention
This invention is directed to a composition and method for removal of photoresist materials from a substrate, such as a flat panel display. Mixtures of a dibasic ester (DBE), an alcohol, a polar organic solvent, and water are used to strip hard to remove photoresist materials, such as photoresist which has been subjected to baking process, without damaging the substrate. The method is effective at low temperatures (50-70xc2x0 C.).
2. Brief Description of the Prior Art
a. Integrated Circuit Processing. Photoresist materials are commonly used as coating masks in the fabrication of integrated circuits. During the fabrication process, photoresist materials are applied to a substrate using various techniques known in the art. The substrate, now coated with photoresist materials, is then exposed with radiation, usually in the UV, e-beam or x-ray wavelengths. After exposure the coated substrate is developed leaving a defined pattern of photoresist materials on the substrate. The photoresist materials that remain on the substrate after developing are used to mask the substrate for further processing. After further processing, the photoresist materials are stripped from the substrate using a photoresist stripper.
Further processing of the photoresist materials after developing, such as high temperature post exposure bake, ion implantation and deep UV radiation hardening lead to highly crosslinked photoresist materials which are extremely resistant to dissolution in most conventionally employed organic strippers. Halogenated and phenolic hydrocarbon solvents have been used to remove these extremely resistant photoresist materials. Use of these types of solvents is undesirable due to the hazards they pose to technicians carrying out the stripping process and due to the potential pollution and environmental problems associated with disposal of the waste product. Alkaline strippers have also been utilized to remove these resistant photoresist materials. Use of these types of strippers is undesirable due to the corrosion they cause to substrates containing metal films, particularly aluminum or various combinations or alloys of active metals such as copper or tungsten.
b. Flat Panel Displays (LCD/TFT). In fabricating large area panels such as LCD/TFT flat panel displays, a glass substrate is coated with photoresist material. The coated substrate is exposed to UV, e-beam or X-ray radiation. After exposure, the coated substrate is developed, leaving a defined pattern of photoresist and open areas on the substrate for further processing. After further processing, the photoresist is stripped from the substrate using a photoresist stripper.
Since the substrate is glass and not a silicon wafer, rinsability is a problem. Large area panels are more susceptible to water rinsing and water induced corrosion than silicon wafers. Therefore, during the rinse cycle thin film metal layers on the FPD can be etched and corroded due to the hydrolysis of alkaline chemicals in strippers that contain organic amines. Metals used in FPD fabrication such as ITO (indium-tin oxide), Mo, Al, Cr vs. Alxe2x80x94Sixe2x80x94Cu, W and Cu, are susceptible to pH and water induced corrosion. In IC manufacturing on silicon wafers, metal layers are about 1000 nm thick, while in LCD/TFT flat panels the thickness of the metal is only 100 nm thick. As a result of thin film thickness difference, what would be minor corrosion and etching of the metal layer for integrated circuits (for example a 50 nm etching) may not affect the yield, but would cause major defect and failure in FPDs.
The flat display panels are normally larger in size than typical silicon wafers. As a result, the processing equipment needed for fabrication of the flat panels is different and the chemical usage for cleaning those panels is much higher than seimiconductor IC manufacturing. The amount of chemical consumption needs to be economically feasible for the FPD industry.
In IC manufacturing, multiple chips are fabricated on a single wafer and when there is a failure on some areas of the wafer, the other areas are still useful. The yield depends on the number of good dies (chips) vs. bad ones on a wafer. However, in FPDs a small defect can cause the failure of an entire panel, which acts as a single device. Therefore, FPD manufacturing requires specialty chemical formulations and finer quality control.
In FPD processing with wet and dry photresist etching, a side wall polymer of cross-linked organo-metallic polymer can be formed around the metallized area of the panel. Removing these side wall polymers without attacking the metal layers requires formulations with particular corrosion inhibitors that are different than conventional alkaline strippers. These stripping compositions remove the photoresist polymers but can damage corrosion sensitive metals.
Because glass substrates cannot tolerate high temperatures like silicon wafers, the adhesion of thin films on glass panels poses a challenge to FPD manufacturing industry. Even small amount of residues can adversely affect the quality of thin films and pose a serious yield loss due to de-cohesion and delamination.
Due to processing limitations, thin films deposited on glass are under higher tensile and compressive stress in comparison to silicon wafers. Chemicals must be formulated to be compatible with stressed thin films to avoid failures.
It is a primary object of the present invention to provide an effective stripping composition for positive photoresist which is water based, non-halogenated, non-phenolic and non-alkaline.
Another object of the present invention is to provide a composition and method for removal of photoresist which is highly effective for removing photoresist from a substrate at low temperatures.
A further object of the present invention is to provide a photoresist removal composition which causes minimal corrosion to substrates and metal films.
Briefly, the preferred embodiments of the present invention utilizes a mixture of a dibasic ester (DBE), an alcohol, a polar organic solvent, and water to remove photoresist from a flat panel substrate. The process is effective at low temperature.